1. Field of Invention
The present invention relates generally to a semiconductor wafer processing system and a method for polishing a substrate.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to stack multiple devices on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
Two exemplary CMP systems that address these issues are described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov et al. and in U.S. Pat. No. 5,738,574, issued Apr. 15, 1998 to Tolles et al., both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization system that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. The transfer station generally contains a load cup that positions the wafer into one of four processing heads mounted to a carousel. The carousel moves each processing head sequentially over the load cup to receive a wafer. As the processing heads fill, the carousel moves the processing head and wafer through the planarization stations for polishing. The wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry or other polishing fluid medium. The polishing pad may include an abrasive surface. Additionally, the slurry typically contains both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Generally, the polishing system is surrounded by an upper enclosure. The upper enclosure isolates the system environment from the surrounding ambient environment and is typically supplied with filtered air, thus minimizing possible substrate contamination. As such, the upper enclosure over the processing area typically contains an exhaust in the ceiling of the enclosure to provide an air return and to vent any gases that may have out-gassed during the polishing process.
Additionally, the lower portion of the system is also enclosed to capture and remove any slurry or other fluids may find their way into the lower portion of the system due to spillage, pad run off or leaks. Slurry and other fluids in the lower portion of the polishing system are generally collected and channeled from the system to a central facility drainage system. However, these slurries or other fluids or their residues may out-gas into the volume defined by the lower portion of the system. Movement of these gases into the upper enclosure from which they may be vented is often slow.
Therefore, there is a need in the art for a system that provides ventilation of the lower portions of a chemical mechanical polishing system.
Generally, the present invention provides a system and method for exhausting a lower region of a chemical mechanical processing system. In one embodiment, the invention provides a base having a first or working side and a second side, and at least one drive system that is disposed on the working side of the base. One or more polishing heads are coupled to the drive system for retaining a workpiece during polishing. A second side enclosure is disposed on the second side of the base and defines a second side volume. A second side exhaust is coupled to the second side volume. When the invention is coupled to a facilities exhaust or other air handler, the second side exhaust ventilates the second side volume.
In another embodiment, the system additionally includes a working side enclosure that is disposed on the working side of the base and defines a working side volume that includes the drive system. A working side exhaust is coupled to the working side volume and can be adapted to ventilate the working side volume.
In another aspect, a method for processing a workpiece is also disclosed. In one embodiment, the method comprises the steps of exhausting a first enclosure through a first exhaust; obtaining a first flow metric indicative of the flow through the first exhaust; exhausting a second enclosure through a second exhaust; obtaining a second flow metric indicative of the flow through the second exhaust; polishing the substrate; monitoring the first and second flow metrics to determine if they fall within a predetermined processing window; and stopping the polishing step if the first flow metric, the second flow metric or the first and second flow metrics fall outside of the window.